Sources of Background Toning in Waterless Lithography.

The waterless lithographic printing behavior of block copolymer masters containing 90% (wt.) poly (dimethyl siloxane) and 10% (wt.) poly (-methylstyrene) was observed in order to characterize the factors affecting the source, structure and evolution of print background as a function of press run length. The primary background ink structure was a filament-like strand (worms). The worms were characterized by a preferred orientation and by a random location on consecutive prints. The background did not lie along the raised paper fibers of the printed sheet and impurities or defects on the master surface were not present in sufficient quantity to account for the background. The production and appearance of print background were: (1) correlated with elastomer softening caused by ink solvent uptake; (2) shown to be significantly influenced by surface splitting patterns on the ink form roll; and (3) demonstrated to be affected by ink rheology, printing speed, printing pressure and ink film thickness. to be significantly influenced by surface splitting patterns on the ink form roll; and (3) demonstrated to be affected by ink rheology, printing speed, printing pressure and ink film thickness.